How Many Euro Breakup Scenarios Are There?

In a short note at Roubini.com, I calculate that there are nearly a quadrillion different permutations for the 17-member eurozone to break up into various single currencies, with a “rump euro” remaining if k>0. What are your views? And is the euro really irreversible, or is that just one possibility out of 1,000,000,000,000,000?